第8章脉冲波形的产生与变换

Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ 8.1 8.1 多谐振荡器多谐振荡器 8.2 8.2 单稳态触发器单稳态触发器 8.3 8.3 施密特触发器施密特触发器 8.4 5558.4 555定时器及其应用定时器及其应用Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ 1、正正确确理理解解多多谐谐振振荡荡器器、单单稳稳态态触触发发器器、施施密密特触发器的电路组成及工作原理。特触发器的电路组成及工作原理。2 2、掌掌握握多多谐谐、单单稳稳、施施密密特特MSIMSI器器件件的的逻逻辑辑功功能能及主要指标计算。及主要指标计算。3 3、掌握、掌握555555定时器的工作原理。定时器的工作原理。4 4、掌掌握握由由555555定定时时器器组组成成的的多多谐谐、单单稳稳、施施密密特特电路工作原理及外接参数及电路指标的计算。电路工作原理及外接参数及电路指标的计算。Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ 8.1.1 门电路组成的多谐振荡器门电路组成的多谐振荡器8.1.2 8.1.2 石英晶体振荡器石英晶体振荡器8.1 8.1 多谐振荡器多谐振荡器 电路的组成及工作原理电路的组成及工作原理 振荡周期的计算振荡周期的计算Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ 多谐振荡器是一种自激振荡器，电路在接通电源后多谐振荡器是一种自激振荡器，电路在接通电源后无需外接触发信号就能产生一定频率和幅值的矩形波脉冲无需外接触发信号就能产生一定频率和幅值的矩形波脉冲波或方波。波或方波。多谐振荡器 VCC8.1 8.1 多谐振荡器多谐振荡器8.1.0 8.1.0 概概 述述Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ 开关电路 延时环节8.1 8.1 多谐振荡器多谐振荡器开关器件开关器件：产生高、低：产生高、低电平；电平；多谐振荡器电路应由哪几部分组成？多谐振荡器电路应由哪几部分组成？反馈延迟环节反馈延迟环节：利用：利用RCRC电电路的充放电特性实现延时，路的充放电特性实现延时，将输出电压恰当地反馈给将输出电压恰当地反馈给开关器件使之改变输出状开关器件使之改变输出状态，以获得所需要的振荡态，以获得所需要的振荡频率。频率。8.1.0 8.1.0 概概 述述Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ 8.1.1 门电路组成的多谐振荡器门电路组成的多谐振荡器 1.1.电路组成电路组成开关器件：开关器件：反馈延迟环节：反馈延迟环节：由由CMOSCMOS门电路组成的多谐振荡器门电路组成的多谐振荡器逻辑门电路逻辑门电路R R、C C 电路电路Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ 8.1.1 门电路组成的多谐振荡器门电路组成的多谐振荡器 2.工作原理工作原理假定假定vO1=1，vO2=0 Vth=VON=VOFF=VDD/2VC进入进入 第二暂稳态第二暂稳态 vIvO1 vO2 vO1VDD0vIVDDVth0vO2VDD0(1)第一暂稳态及第一暂稳态及电路自动翻转过程电路自动翻转过程 01 Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ 门电路组成的多谐振荡器门电路组成的多谐振荡器vO1=0，vO2=1 Vth=VON=VOFF=VDD/2(2)(2)第二暂稳态及第二暂稳态及电路自动翻转过程电路自动翻转过程 二二vO1VDD0vIVDDVth0vO2VDD0T1T2vI vO1 vO 10 2.工作原理Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ 3.3.振荡周期振荡周期T T的计算的计算vO1VDD0vIVDDVth0vO2VDD0T1T2TRC1n41.4RC T =T1(充充)+T2(放放)8.1.1 8.1.1 门电路组成的多谐振荡器门电路组成的多谐振荡器Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ 4、加补偿电阻的、加补偿电阻的CMOSCMOS多谐振荡器多谐振荡器R RON(P)+RON(N)电源电压波动时，会使振荡频率不稳定电源电压波动时，会使振荡频率不稳定。RSC C分布分布（分布电容）（分布电容）8.1.1 8.1.1 门电路组成的多谐振荡器门电路组成的多谐振荡器，RsR(一般取一般取 Rs=10R)。当当Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ 8.1.2 石英晶体振荡器石英晶体振荡器由门电路组成的多谐振荡器，周期由门电路组成的多谐振荡器，周期 T 取决于取决于R C 和和 Vth，频率稳定性较差。频率稳定性较差。电路符号电路符号 阻抗频率特性阻抗频率特性 R R：使反相器工作在线性放大区使反相器工作在线性放大区 C C1 1：两个反相器间的耦合两个反相器间的耦合 C C2 2：抑制高次谐波，以保证稳定的频率输出。抑制高次谐波，以保证稳定的频率输出。石英晶体振荡器石英晶体振荡器优点：振荡频率稳定性高，常用作基准信号源优点：振荡频率稳定性高，常用作基准信号源1 1、石英晶体振荡器电路、石英晶体振荡器电路Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ 2、石英晶体振荡器应用、石英晶体振荡器应用8.1.2 8.1.2 石英晶体振荡器石英晶体振荡器Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ 8.2.1 门电路组成的微分型单稳态触发器门电路组成的微分型单稳态触发器8.2.2 8.2.2 集成单稳态触发器集成单稳态触发器8.2.3 8.2.3 单稳态触发器的应用单稳态触发器的应用8.2 8.2 单稳态触发器单稳态触发器Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ 电路有一个稳态，一个暂稳态。电路有一个稳态，一个暂稳态。一、单稳态触发器的工作特点：一、单稳态触发器的工作特点：8.2 8.2 单稳态触发器单稳态触发器 在外来触发信号作用下，电路由稳态翻转到暂稳态在外来触发信号作用下，电路由稳态翻转到暂稳态;电路中电路中RCRC延时环节的作用，暂稳态不能长久保持延时环节的作用，暂稳态不能长久保持,经过一段时间后，电路会自动返回到稳态。暂稳态的经过一段时间后，电路会自动返回到稳态。暂稳态的持续时间仅取决于持续时间仅取决于RCRC电路的参数值。电路的参数值。概述概述Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ 8.2 单稳态触发器单稳态触发器由门电路和由门电路和 R CR C电路组成电路组成三、三、单稳态触发器的分类单稳态触发器的分类概述概述根据根据RCRC电路的不同接法电路的不同接法单稳态触发器单稳态触发器分为分为微分型微分型和和积分型积分型两大类。两大类。Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ 用用CMOS门电路组成的微分型单稳态触发器门电路组成的微分型单稳态触发器 1.1.电路电路CMOS与非门构成的微分型与非门构成的微分型单稳态触发器单稳态触发器 CMOS或非门构成的微分型或非门构成的微分型单稳态触发器单稳态触发器 稳态为稳态为1正脉冲触发正脉冲触发稳态为稳态为0负脉冲触发负脉冲触发 Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ vO1vO2vcvIRvRvDD0 00 00 01 11 18.2.1 8.2.1 门电路组成的门电路组成的微分型单稳态触发器微分型单稳态触发器Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ v R vO2 vIvR vO2 vO1 vO1vO2vcvIRvRvDD1 11 11 11 10 08.2.1 8.2.1 门电路组成的微门电路组成的微分型单稳态触发器分型单稳态触发器b)b)外加触发信号后，电路进外加触发信号后，电路进入暂稳态入暂稳态c)c)电容放电，电路由暂稳态电容放电，电路由暂稳态自动返回到稳态自动返回到稳态0 0Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ tw w (2)(2)恢复时间恢复时间t trere tre 3 d(3)(3)最高工作频率最高工作频率 f fmaxmax 8.2.1 8.2.1 门电路组成的微分型单稳态触发器门电路组成的微分型单稳态触发器 R(t)=VR()VR(0+)VR()R(0+)=0 R()=VDD =RCDepartment of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ D D大于大于G G1 1的开门电平的开门电平(V(VONON)。8.2.1 8.2.1 门电路组成的微分型单稳态触发器门电路组成的微分型单稳态触发器电阻电阻R R的取值可以是任意的取值可以是任意的吗？的吗？采用采用TTLTTL与非门构成单稳电路时，电阻与非门构成单稳电路时，电阻R R要小于要小于0.7k0.7k。在暂稳态结束在暂稳态结束(t=t(t=t2 2)瞬间，瞬间，门门G G2 2的输入电压的输入电压 R R达到达到V VDDDD+V+VT T，可能损坏可能损坏G G2 2门，怎门，怎么办？么办？输入的触发脉冲的宽度可以是输入的触发脉冲的宽度可以是任意的吗？如触发脉冲的宽度任意的吗？如触发脉冲的宽度太宽会有什么问题？太宽会有什么问题？Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ 8.2.2 集成单稳态触发器集成单稳态触发器vOvItwtwvOvItwtw不可重复触发不可重复触发可重复触发可重复触发被重复触发被重复触发不可重复触发不可重复触发Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ 1.1.不可重复触发的集成单稳态触发器不可重复触发的集成单稳态触发器 74121741211G8G4G1G2G3G5G6G7G8&B&1111RextRintCextRintCext/RextA1A2a触发信号控制电路触发信号控制电路微分型单稳触发器微分型单稳触发器输出缓冲电路输出缓冲电路BCextRintCext/RextA1A2GNDNCNCNCVCCNC8.2.2 8.2.2 集成单稳态触发器集成单稳态触发器 (1)(1)工作原理工作原理1G8G4G1G2G3G5G6G7G8&B&1111RextRintCextRintCext/RextA1A2a电路稳态电路稳态 :Q Q=0,=0,0 01 10 00 00 0 在暂稳态期间即使有触发信号输入，在在暂稳态期间即使有触发信号输入，在a a点不产生触发脉冲，只有等电路返回点不产生触发脉冲，只有等电路返回稳态后，电路才会被再次触发，电路属于不可重复触发单稳态触发器。稳态后，电路才会被再次触发，电路属于不可重复触发单稳态触发器。8.2.2 集成单稳态触发器集成单稳态触发器1.1.不可重复触发的集成单稳态触发器不可重复触发的集成单稳态触发器 7412174121电路暂稳态电路暂稳态 :Q Q=1,=1,输出脉冲宽度：输出脉冲宽度：tw0.7RCtw0.7RC Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ 两种触发方式两种触发方式 BCextRintCext/RextA1A2GNDNCNCNCVCCNC定时电容定时电容定时电阻定时电阻用内部用内部2k2k电阻电阻用外部电阻用外部电阻HHA1A2BQLXHLXLHLXXLLHHHXLHHHHHHLXXL8.2.2 8.2.2 集成单稳态触发器集成单稳态触发器1.1.不可重复触发的集成单稳态触发器不可重复触发的集成单稳态触发器 7412174121（3 3）电路连接）电路连接Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ G1111G G1212G G1010G G1313G G1414G G1515G G1616G G1 1G G2 2G G3 3G G4 4G G5 5G G6 6G G7 7G G8 8G G8 8&1 11 11 11 11 11 11 11 11 11 11 11 1R Rextextv vc cv vDDDDC Cextextv vDDDDTRTR+TRTR-R RD DT TP PT TN Nv v1212v v1010v vo4o4v vo7o7三态门三态门控制电路控制电路输出缓冲电路输出缓冲电路(1)(1)电路电路8.2.2 8.2.2 集成单稳态触发器集成单稳态触发器Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ 1C Ce e x x t tc c1R1Rextext/C/Cextext1R1RD D1 1TRTR+1 1TR_TR_V VssssV VDDDD2C2Cextext2R2Rextext/C/Cextext2R2RD D2 2TRTR+2 2TR_TR_功能表功能表单单 稳稳单单 稳稳H H禁禁 止止H HL LL L禁禁 止止H HL LH H清清 零零H HL LL LQ QTRTRTRTR功能功能 输输 出出 输输 入入H HH HL L引脚图引脚图8.2.2 8.2.2 集成单稳态触发器集成单稳态触发器Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ t1 1TRTR+TRTR-0 00 00 00 0V VC CV Vth13th13V Vth8th8t t2 2t t3 3t t4 4t t5 5t t6 6t t7 7t tw wt tw wt t+t tw wt tt tt tt t脉冲宽度包括电容充电和放电两段。脉冲宽度包括电容充电和放电两段。8.2.2 8.2.2 集成单稳态触发器集成单稳态触发器Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ 8.2.3 单稳态触发器的应用单稳态触发器的应用1.1.定时定时 t tw wt t w wAABextCextR1274121(0)R1extCVCCC1vIvO0QAABextCextR1274121(1)R2extCVCCC2vOQVCC2.延时延时0tvI0tvo00tvotw1tw1用两片用两片74121组成脉冲延时电路组成脉冲延时电路,从波从波形图可以看出形图可以看出,vo脉冲的上升沿相对脉冲的上升沿相对输入信号输入信号vI的的上升沿延迟了上升沿延迟了tw1时间。时间。H HH HA A1 1A A2 2B BQ QL LX XH HL LX XL LH HL LX XX XL LL LH HH HH HX XL LH HH HH HH HH HH HL LX XX XL LDepartment of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ R1 1C C1 1 8.2.3 8.2.3 单稳态触发器的应用单稳态触发器的应用v vccccB BA A1 1 A A2 2v vccccS SR R1 1R R2 2C C1 1C C2 2C CextextC Cextext/R/RextextC CextextC Cextext/R/Rextext7412174121()7412174121()v vo ov vccccv vccccB B A A1 1 A A2 2v vcccc3 3.组成多谐振荡器组成多谐振荡器 0 00 0H HH HA A1 1A A2 2B BQ QL LX XH HL LX XL LH HL LX XX XL LL LH HH HH HX XL LH HH HH HH HH HH HL LX XX XL L0 01 11 1 0 01 1 0 0单稳单稳进入暂稳态，脉宽为进入暂稳态，脉宽为0.70.7R R2 2C C2 2 1 1 0 0单稳单稳进入暂稳态，脉宽为进入暂稳态，脉宽为0.70.7R R1 1C C1 1 单稳单稳进入暂稳态，脉宽为进入暂稳态，脉宽为0.70.7R R2 2C C2 2 T T=0.7(=0.7(R R1 1C C1 1+R R2 2C C2 2)Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ 8.2.3 单稳态触发器的应用单稳态触发器的应用R RC CC CextextC Cextext/R/Rextext7412174121v vo ov vccccB B A A1 1 A A2 2v vI IC1C1D DR R4 4.组成噪声消除电路组成噪声消除电路 噪声噪声 v vo ov vI ID DCPCP(R)(R)v vo ov vI I噪声多表现为尖脉冲，宽度较窄，而有用的信号的宽度较宽。噪声多表现为尖脉冲，宽度较窄，而有用的信号的宽度较宽。注意：单稳触发器的输出脉宽应大于噪声宽度注意：单稳触发器的输出脉宽应大于噪声宽度 而小于信号脉宽，才可消除噪声。而小于信号脉宽，才可消除噪声。Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ 8.3.1 8.3.1 门电路组成的施密特触发器门电路组成的施密特触发器 8.3.2 8.3.2 集成施密特触发器集成施密特触发器CC40146CC401468.3 8.3 施密特触发器施密特触发器 电路的组成及工作原理电路的组成及工作原理 振荡周期的计算振荡周期的计算 8.3.3 8.3.3 施密特触发器的应用施密特触发器的应用Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ 8.3 施密特触发器施密特触发器施密特触发器的工作特点：施密特触发器的工作特点：施密特触发器属于电平触发器件，适用于缓慢变化的信号，施密特触发器属于电平触发器件，适用于缓慢变化的信号，当输入信号达到某一定电压值时，输出电压会发生突变。当输入信号达到某一定电压值时，输出电压会发生突变。电路有两个阈值电压。电路有两个阈值电压。输入信号增加和减少时，电路的阈值输入信号增加和减少时，电路的阈值电压不同，电路具有如下图所示的传输特性电压不同，电路具有如下图所示的传输特性 。v vo ov vI Iv vo ov vI IDepartment of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ 8.3.1 门电路组成的施密特触发器门电路组成的施密特触发器v v I1I1v vo ov vI IR R1 1 R R2 2 I I为三角波为三角波 作如下假定：作如下假定：Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ 8.3.1 门电路组成的施密特触发器门电路组成的施密特触发器v vI1I10 00 0只要只要v vI1I1 V Vthth，则保持则保持v vO O=V VOHOH当当v vI1I1=V Vthth，电路产生如下正反馈电路产生如下正反馈 ：当当v vI I下降下降，v vI1I1也也下降下降0 0回差电压回差电压 v vI I v vI I1 1 v vO O 1 1 v vO O Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ 8.3.1 门电路组成的施密特触发器门电路组成的施密特触发器v vI IV VT+T+V VT_T_v vO O0 00 0t tt t0 0v vI Iv vO OV VT+T+V VT_T_V VDDDD(a)(a)工作波形工作波形(b)(b)传输特性曲线传输特性曲线v vI1I1Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ 8.3.2 集成施密特触发器集成施密特触发器-CC40146-CC40146v vo ov vDDDDv vI IT TP1P1T TN4N4T TP2P2T TP3P3T TP7P7T TP11P11T TN5N5T TN6N6T TN8N8T TN10N10T TP8P8T TN12N12vvO O施密特触发器施密特触发器 整形级整形级 输出缓冲级输出缓冲级 V VT+T+V VT_T_v vo ov vI IDepartment of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ 8.3.3 施密特触发器的应用施密特触发器的应用1.1.波形的整形及变换波形的整形及变换 v vo ov vI Iv vo ov vT2T2v vT1T1t tt tt t合理选择回差电压，可消除干扰信号。合理选择回差电压，可消除干扰信号。为去掉干扰信号为去掉干扰信号回差电压应如何选择？回差电压应如何选择？Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ 8.3.3 施密特触发器的应用施密特触发器的应用2.2.幅度鉴别幅度鉴别v vo ov vI I0 00 0t tt tV Vthth(V VT+T+)Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ 8.3.3 施密特触发器的应用施密特触发器的应用2.2.多谐振荡器多谐振荡器 C Cv vo ov vI IR R1 1v vo ov vI IV VT+T+V VT_T_V VOLOLV VOHOHT T1 1T T2 20 0t t0 0t tDepartment of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ 8.4.1 5558.4.1 555定时器定时器 8.4.2 8.4.2 定时器应用举例定时器应用举例8.4 5558.4 555定时器及其应用定时器及其应用 电路的组成电路的组成 用用555555定时器组成定时器组成单稳态触发器单稳态触发器 用用555555定时器组成定时器组成多谐振荡器多谐振荡器 用用555555定时器组成定时器组成施密特触发器施密特触发器 工作原理工作原理Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ 5558.4.1 555定时器定时器电阻分压器电阻分压器电压比较器电压比较器基本基本RSRS触发器触发器复位输入端复位输入端(0)(0)输出缓冲反相器输出缓冲反相器集电极开路输出三极管集电极开路输出三极管T Tv vo ov vICICv vI1I1v vI2I2v vo oC C1 1C C2 2+-+(1)(1)(2)(2)(3)(3)(4)(4)(5)(5)(6)(6)(7)(7)R RS S&5 k5 k 5 k5 k 5 k5 k&1 1R RD DV VCCCC(8)(8)G G1 1、电路组成、电路组成Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ 01 10 08.4.1 8.4.1 555555定时器定时器T Tv vo ov vICICv vI1v vI2v vo oC C1 1C C2 2+-+(1)(1)(2)(2)(3)(3)(4)(4)(5)(5)(6)(6)(7)(7)R RS S&5 k5 k 5 k5 k 5 k5 k&1 1R RD DV VCCCC(8)(8)G G 如果悬空如果悬空0 01 10 01 10 01 10 01 11 10 01 11 11 1保持保持保持保持2 2、工作原理、工作原理Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ 555555定时器功能表定时器功能表不变不变不变不变1 1导通导通0 01 1截止截止1 11 1导通导通0 00 0放电管放电管T T输出输出(V VO O)复位复位(R RD D)触发输入触发输入(V VI2I2)阈值输入阈值输入(V VI1I1)输输 出出输输 入入8.4.1 8.4.1 555555定时器定时器Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ 四四 占空比可调的多谐振荡器电路占空比可调的多谐振荡器电路 利利用用半半导导体体二二极极管管的的单单向向导导电电特特性性，把把电电容容C充充电电和和放放电电回回路路隔隔离离开开来来，再再加上一个电位器，便可构成占空比可调的多谐振荡器。加上一个电位器，便可构成占空比可调的多谐振荡器。可计算得可计算得：T1=0.7R1C T2=0.7R2C 占空比：占空比：Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/ 0截止截止1 1导通导通0 0 T T V VO OV VI2I2V VI1I1输输 出出输输 入入0 01 13 3V VCCCC2 23 3V VCCCCv vI Iv vO OV VOHOHDepartment of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science Department of Electronics and Information Science http:/http:/